Field of the Invention
The invention relates to a multi-way slide-type shutoff valve for suction air of suction-type grippers on a sheet-transfer drum and, more particularly, to such a valve which is usable in sheet-fed rotary printing presses wherein sheet-transfer drums are provided for the transport of sheets, a respective sheet being held in grippers on the sheet-transfer drums, and at least some of the grippers being in the form of suction-type grippers.
Whenever there is a job change in order to print sheets of a different size or format, it is advantageous to adapt the position of the suction-type grippers on the outer cylindrical surface of the sheet-transfer drum to suit the new size or format to be printed. For this purpose, devices for adjusting the position of the suction-type grippers are used, such devices enabling individual or group-wise adjustment of the suction-type grippers in the rotational direction and perpendicularly to the rotational direction of the sheet. Simultaneously with the adjustment of the position of the suction-type grippers, it is possible for the sheet-holding surface on the outer cylindrical surface to be adapted to suit the new sheet size to be printed.
The suction-type grippers which, for reasons inherent to the design or construction, cannot be adjusted to the new sheet size or format must be rendered inoperative in order to maintain the vacuum generated by a suction-air source.
In simple devices, the suction air of each suction-type gripper situated outside of the sheet to be transported can be switched off manually by means of a valve. Such manual operations are time-consuming and are difficult to perform because of the restricted access to the shut-off valves, particularly when there are a plurality of groups of suction-type grippers, disposed in rows, on sheet-transfer drums of double- or multiple-size diameter, as compared with the diameter of the impression or blanket cylinder, for example.
In a sheet-fed rotary printing press with a plurality of sheet-transfer drums, the time required to change the suction-type grippers over is multiplied. In addition, there is the danger of incorrect adjustments when the change-over is performed manually.
The Japanese Patent 4-161336 describes a suction-air device for a transfer drum containing two slide-type shutoff valves for pair-wise shutting-off the suction air of suction-type grippers on a drum. The slide-type shutoff valves are each formed of a displaceable closing tube, which has air passages for inlet and outlet air. The air passages are rectangular in form and correspond with openings of a tube serving as a housing, the openings being connected to the intake ducts of suction-type grippers. A disadvantage of this device is that the closing tube is expensive to manufacture due to the rectangular penetrations and the relatively large sealing surface.
A similar device is also described in the Japanese Patent 4-158041. Two closing elements are provided in a suction tube, the closing elements being simultaneously displaceable inside the suction tube with the aid of a threaded spindle. The suction-air connection is situated approximately in the center of a transfer drum, so that the suction-air holes of suction-type grippers, the suction-air holes being situated further to the outside in relation to the respective closing element, have no connection to a suction-air source. A disadvantage of this device is that, when suction-type grippers are being rendered inoperative, the closing elements have to cover long adjustment distances, which requires a long adjustment time, and the fact that such adjustment mechanisms are required separately for each row of suction-type grippers, which signifies increased expense.